In a state where a tire contacts the ground, tubular space is formed by a main groove extending in the tire circumferential direction and a road surface. The rotation of tires lets air compressed in the tubular space to release outside, resulting in generating air columnar resonance noise. Since the air columnar resonance noise is offensive noise whose frequency is around 1 kHz, reduction in air columnar resonance noise has been demanded conventionally. For example, the pneumatic tire disclosed in the patent document 1 has a great number of oblong holes that extend in the depth direction of a main groove formed in a sidewall of the main groove. With the oblong holes, friction resistance against the air flow in the main groove increases and as a result, air columnar resonance noise is reduced.
Patent Document 1: Unexamined Japanese Laid-Open Patent Publication No. 10-315711 (FIG. 1)